bugGNU Octave - Bugs: bug #39535, FaceAlpha property not working for...


bug #39535: FaceAlpha property not working for OpenGL backend

Submitted by:  Rik <rik5>
Submitted on:  Fri Jul 19 23:01:35 2013  
Category: Plotting with OpenGLSeverity: 3 - Normal
Priority: 5 - NormalItem Group: Incorrect Result
Status: Patch SubmittedAssigned to: None
Originator Name: Open/Closed: Open
Release: devOperating System: Any

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Sun Mar 12 17:13:21 2017, comment #5:

Attached is a patch that adds some very primitive support for alpha on faces of patch objects. It does not include any sorting primitives. However, it might give better results than the current implementation (which hides patches with alpha != 0) in very simple cases as the ones from bug #50520:

or bug #46538:

or the one in comment #0.

Since no sorting primitives are included, it fails with more complex layouts as in:

It also only adds support for double valued "FaceAlpha". "flat" or "interp" skip rendering the faces (like without the patch).

Even if this is by far no complete implementation of transparency, this very limited support might be helpful in some use cases.

(file #39977)

Markus M├╝tzel <mmuetzel>
Project Member
Fri Nov 18 15:32:57 2016, comment #4:

This bug is still present in the current dev 4.3.0 (39f39eb4e476).

Pantxo Diribarne <pantxo>
Project Member
Sat Sep 12 22:22:41 2015, comment #3:

I am pinging this report as it is still valid.

facealpha < 1 doesn't render in opengl graphics toolkits (fltk, qt)

Juan Pablo Carbajal <juanpi>
Fri Jul 19 23:58:32 2013, comment #2:

Rats! I had thought it might be something simple like not passing a parameter over to OpenGL. I see that it is definitely non-trivial. I'll leave the bug report open as a placeholder.

Rik <rik5>
Project Administrator
Fri Jul 19 23:29:19 2013, comment #1:

Support for transparency is globally not implemented yet in the OpenGL renderer. Although, transparency effects are possible in OpenGL, it's not trivial and requires sorting primitives from back to front [1]. I had some implementation in JHandles, but I never ported it to octave, IIRC I found is sub-optimal.

This was a suggestion for a GSoC project, but it wasn't picked up.

[1] http://www.opengl.org/archives/resources/faq/technical/transparency.htm

Michael Goffioul <goffioul>
Project Member
Fri Jul 19 23:01:35 2013, original submission:

The FaceAlpha property determines the transparency of a face. The FLTK backend, however, interprets everything that is not 1 (opaque) as 0 (transparent). The property works with gnuplot.

Example code:

This seems like it should be possible since OpenGL can handle all kinds of strange colors/alpha blends.

Rik <rik5>
Project Administrator


(Note: upload size limit is set to 16384 kB, after insertion of the required escape characters.)

Attach File(s):

Attached Files
file #39977:  bug39535_patch_facealpha.patch added by mmuetzel (2kB - application/octet-stream)


Depends on the following items: None found

   bug dependencies.


Carbon-Copy List
  • -unavailable- added by mmuetzel (Updated the item)
  • -unavailable- added by pantxo (Posted a comment)
  • -unavailable- added by juanpi (Posted a comment)
  • -unavailable- added by goffioul (Posted a comment)
  • -unavailable- added by rik5 (Submitted the item)

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    Follow 6 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Sun Mar 12 17:13:21 2017mmuetzelAttached File-=>Added bug39535_patch_facealpha.patch, #39977
      StatusConfirmed=>Patch Submitted
      Operating SystemGNU/Linux=>Any
    Sun Mar 12 14:47:25 2017mmuetzelDependencies-=>bugs #50520 is dependent
    Thu Nov 26 16:02:04 2015rik5Dependencies-=>bugs #46538 is dependent
    Sun Dec 28 15:47:31 2014rik5StatusNone=>Confirmed

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